Cortical regions with well-defined layers and cell types offer valuable models for insights into the neural basis of brain function. The olfactory bulb is attracting increasing interest for this purpose. We will test critical hypotheses for the sequence of operations that underlie the perception of smell, using new methods that we have developed during the current grant period. The experiments will be carried out on wild type rats and mice and on mice transfected with a gene for a specific olfactory receptor tagged with green fluorescent protein to make it visible during the experiments under infrared and confocal 2-photon microscopy. Odor reception will be analyzed by excising "swatches" of the olfactory epithelium and characterizing in detail their odor responses with patch recordings and Ca imaging. We will test the hypothesis that receptor cells with similar odor responses have a neighboring distribution within the olfactory epithelium. Odor mapping in the glomerular layer of the olfactory bulb will be carried out using newly developed high resolution fMRT; we will test the hypothesis that receptor-labeled glomeruli have similar response properties as receptor-labeled receptor cells. Dendritic integration involved in reception and processing in the glomerular tuft of mitral cells will be analyzed; we hypothesize that critical membrane and synaptic properties give rise to regenerative responses that increase the signal-to-noise ratio, which produce intense activity foci in the glomeruli. Computational models of the results will be made web accessible through databases supported by other grants. The results will deepen our understanding of the information processing properties of dendrites and microcircuits and the neural basis of smell perception in health and disease.